Rotational viscometers require a rotating element called the rotor and a stationary element in fluid contact with the rotor which stationary element is called the stator. Most often the rotor turns within the stator. Sensitive rotatational viscometers such as the Brookfield viscometer are well-known instruments for measuring viscosities of liquids. Usually, the rotor, which is driven by the Brookfield head, is immersed in a large container of liquid in which the walls of the container are at some considerable distance from the rotor and thus have little influence on the measurement of the viscous value. However, in some applications such as in the well-known Scanning Brookfield Technique used in ASTM D 5133, incorporated herein by reference as its 1990 version, the rotor must be relatively close to the stator wall to gain the necessary sensitivity. In such a case, the rotor must be centered very carefully.
This Scanning Brookfield Technique, discovered and developed by Mr. Theodore W. Selby and licensed to the Tannas Co., Midland, Mich., was improved by a support and centering device disclosed by Deysarkar et al., U.S. Pat. No. 4,648,263 (Mar. 10, 1987), incorporated herein by reference.
In practice, problems are encountered with the comercially available support and centering attachment as of Deysarkar et al., which is known commercially as the Pennzoil/Tannas rotor/stator centering adapter, Tannas Model Number SBV-P. In particular, and in reference to the foregoing patent, in a centering device 40 for sensitive rotating viscometer 10 having a cylindrical lower end of pivot housing 20 and rotor 24, particularly in the Model Number SBV-P adapter, an O-ring 00, present in the SBV-P adapter in a slot cut in interior surface 54 of cylindrical member 70, can swell as from contact with solvents or oil to the point where sometimes, upon the contraction of the constraining cylindrical member 70, a glass stator 28 may break. The O-ring also may become worn or oily, and, if a loose fit between cylindrical member 70 and stator 28 is engendered, slippage and rotation of the stator occurs during testing which destroys the value of the test. Furthermore, the O-ring can be difficult to install and remove for replacement. Another effect of low-temperature contraction of cylindrical member 70 is that when bath 44 controls the temperature of test liquid 26 at minus 40 degrees C., or below, separation of parts of device 40, to include removal of a glass stator 28, which has annular lip 56, the stator being filled with tested liquid, from the lower end 52 of the device, becomes very difficult because of the aforementioned contraction of the engineering thermoplastic employed to make the adapter. Other problems exist.
What is needed is an adapter which overcomes such problems while providing for precise centering of the rotor spindle in the stator of a sensitive rotating viscometer. The adapter should be readily manufacturable--and be efficient to operate, especially by even inexperienced operators.